AUCKLAND, New Zealand (AP) _ Bristling at international criticism, Nigeria's foreign minister said today that a prominent activist sentenced to death is not a political prisoner but a criminal responsible for four ``gruesome murders.''

The 52 Commonwealth nations meeting here _ Britain and many of its former colonies _ issued a joint appeal for clemency to their Commonwealth partner today to spare the life of Nigerian playwright Ken Saro-Wiwa, whose criticism of Nigeria's vital oil industry for polluting tribal lands has angered the country's military regime.

Nigeria insisted the sentence was warranted.

``We should not misjudge what has happened and imagine that Saro-Wiwa is being persecuted because he is worrying about the environment,'' said its foreign minister, Chief Tom Ikimi. ``People ask if a trial for murder became a trial of civil rights or politics. This is not the truth.''

Saro-Wiwa, 54, was convicted Oct. 31 in the deaths of four men during a May 1994 political rally, but says he was framed. He is one of dozens of activists jailed by Gen. Sani Abacha's regime.

Saro-Wiwa and eight others convicted are from the Ogoni ethnic group, a 500,000-strong minority in southern Nigeria who say their land and water have been destroyed by oil-industry pollution.

``Unfortunately, Mr. Ken Saro-Wiwa ... did not want to use civilized means of normal negotiations to achieve his ends,'' Ikimi said. ``He was responsible along with others for the gruesome murders of four of the members of that movement who were the original leaders.''

Saro-Wiwa's execution appeared imminent today with reports that executioners had been sent to his prison Thursday in the southern city of Port Harcourt. Newspapers in Lagos, Nigeria's commercial capital, reported today that the executioners were turned away because their paperwork was not in order.

Defending his own country's legal system, Ikimi said: ``There is capital punishment in other countries of the world.''

Commonwealth leaders begin private talks Saturday on how to deal with Abacha, who seized power in a 1993 coup. Some have suggested imposing sanctions against Nigeria such as those used against South Africa's former apartheid regime. But the proposal puts some in a difficult position.

Nigeria spearheaded the anti-apartheid campaign that helped free Nelson Mandela from decades of imprisonment, leading eventually to his election last year as the country's first black president.

In his first appearance today as president before the Commonwealth, Mandela thanked the group for inspiring ``a universal offensive against the evil system of apartheid.''

South Africans, he pledged, will ``not stand aside when any people anywhere in the world become victim to systemic racism, oppression and tyranny.''

However, on Thursday Mandela indicated that he was not ready to call for sanctions against Nigeria ``at this stage,'' preferring to issue a warning first.

``If, of course, persuasion does not succeed, then there will be time enough to consider other options,'' he said.

The Clinton administration has denounced the death sentences and said Nigeria must make a ``swift and credible'' move toward democracy.